Monday, October 3, 2011

Spindle cell lipomas are benign tumors in which mature fat is replaced by collagen-forming spindle cells. Pleomorphic lipoma is a variant of spindle cell lipoma that contains a marked cellular pleomorphism and scattered bizarre giant cells. Histologically, these lesions may be difficult to differentiate from liposarcoma.

Patients present with a solitary, well-circumscribed nodule that is slow-growing and painless. Patients are most often men between 45 and 65 years of age. Multiplicity of lesions is uncommon, with several cases of familial and nonfamilial multiple spindle cell lipomas in the literature (incidentally, all of these occurred in male patients).

The lesions are most commonly located in subcutaneous fat of the posterior neck and shoulder area. An intramuscular location is uncommon. Occurrence in the lower extremity should suggest a different diagnosis, as it is an extremely rare presentation.

Imaging findings are nonspecific and can mimic those of liposarcoma. Spindle cell lipomas are complex fatty mass masses with variable lipomatous and nonlipomatous
components. The finding of a well-defined complex fatty mass located in the subcutis (especially in the posterior neck or shoulder) of a middle-aged man should suggest the diagnosis.

The images above are from a 55-year-old man who presented with a 3-year history of a slowly growing left shoulder mass. The lesion is heterogeneously hypoechoic on ultrasound and contains foci of fat attenuation on CT. The foci of fat are better seen on the T1-weighted images as hyperintense spots that lose signal with fat saturation (PD and T1 post-contrast). The bulk of the lesion, however, is T1-hypointense, T2-hyperintense, and avidly enhancing.